Which muscle forcefully closes the jaw and is also superficial?

Correct Answer: D

Rationale: The masseter forcefully closes the jaw during chewing and is superficial, lying over the mandible's ramus, easily palpable. Temporalis, also a jaw closer, is deeper under the scalp. Lateral pterygoid protrudes and depresses the jaw, not closing it forcefully, and is deep. Medial pterygoid closes the jaw but is deep to the masseter. Masseter's superficial position and power make it the correct answer, as it's the primary, visible jaw-closing muscle, vital for mastication.

Correct Answer: D

Rationale: Exercise strengthens muscles by stressing fibers, prompting growth and repair. Resistance training or cardio increases muscle mass, endurance, and power through repeated contraction and recovery. Diet and food provide nutrients protein, carbs but without exercise, they don't build strength directly, only support it. Sleeping aids recovery, allowing muscle repair, but doesn't actively strengthen. Exercise's mechanical stress triggers hypertrophy, enhancing fiber size and efficiency, unlike diet's passive fuel role or sleep's restorative one. Regular activity, like lifting or running, directly fortifies muscles, making it the primary driver, supported but not replaced by nutrition and rest, critical for physical capability.

Correct Answer: D

Rationale: Joints that are fibrous and immovable are classified as synarthroses, such as skull sutures, where dense connective tissue binds bones tightly, ensuring stability with no motion. Tendons connect muscles to bones, and tibia is a bone neither are joint types. Ligaments link bones, and femur is a bone, but this pairing doesn't define a joint category. Diarthrosis refers to freely movable synovial joints, like the knee, opposite to the question's intent. Synarthroses accurately describe fibrous, fixed joints, critical for structures requiring rigidity, like the cranium, distinguishing them from movable or cartilaginous joints in anatomical classification.

Correct Answer: C

Rationale: Myosin, the thick filament in sarcomeres, features cross-bridges protruding heads that bind actin during contraction. These bridges, powered by ATP, pull actin inward, driving the power stroke. Troponin, on thin filaments, binds calcium to regulate contraction, lacking bridges. Actin forms thin filaments, receiving cross-bridges, not bearing them. Tropomyosin shields actin's sites, also without bridges. Myosin's cross-bridges are unique, enabling force generation, distinguishing it from actin's structural role or troponin and tropomyosin's regulatory functions, essential for the sliding filament mechanism and muscle movement.

Correct Answer: C

Rationale: Hypertrophy is muscle size increase from training, as resistance stress thickens fibers via protein synthesis, enhancing strength and mass, like in weightlifting. Atrophy is size loss from inactivity, opposite to training's goal. Fatigue is temporary exhaustion, not size change. Hyperplasia, fiber number increase, is rare in humans, unlike hypertrophy's fiber growth. This adaptation reflects muscle's response to mechanical overload, distinct from shrinkage, energy depletion, or theoretical cell addition, central to exercise-induced development.